An internal combustion engine combusts a mixture of air and fuel within cylinders to generate drive torque. For each type of fuel, there is an optimal ratio of air/fuel that results in complete combustion. This is also known as a stoichiometric air/fuel ratio. Airflow and fueling is regulated based on feedback from various sensors in an effort to maintain this stoichiometric air/fuel ratio. Lean operation refers to the combustion of fuel with an excess of air (i.e., a higher than stoichiometric air/fuel ratio). Lean operation is typically diagnosed as a fault because it requires higher ignition temperatures and therefore sometimes results in misfires. The cause of a lean operation fault, however, could be one of a variety of components malfunctioning. This often results in a non-malfunctioning component being replaced during servicing, which increases service time and warranty costs. Accordingly, while such fuel system diagnostics do work well for their intended purpose, there remains a need for improvement in the relevant art.